HISTOCHEMICAL AND HISTOPHYSICAL INVESTIGATIONS ON THE ACETYLATION BLOCKADE OF CARBOXYLIC GROUPS OF POLYSACCHARIDES

Acetylation abolishes the metachromatic staining of certain mucins, specifically of those that stain metachromatically at pH 2.3-3.0 and in which the metachromasia is produced by oxidation with chromic acid. Mucopolysaccharides that stain metachromatically at pH 1.5 or after sulfation stain metachromatically even after acetylation. Neuraminidase treatment abolishes in some substrates (demilunes of the submandibular gland of Canis familiaris, mucous cells of the submandibular gland of Bos taurus and Ovis aries) the chromotropy and alcianophilia, whereas in others (mucous cells of the submandibular gland of Canis familiaris, demilunes of the submandibular gland of Felis catus) it causes only a weakening of these reactions, which disappear after successive acetylation. Infrared spectra of histologic sections show the appearance of a peak at 1730 cm –1 after acetylation. These studies indicate that acetylation blocks the carboxylic groups of sialic acids or of other mucins and neuraminidase-resistant sialic acid-containing substances. Infrared spectrophotometric analysis shows the presence of ester linkages upon acetylation, but does not exclude the possible formation of δ-lactones.